The present invention relates to a thin film magnetic head used for recording/reproducing of a magnetic disk drive or the like, in particular a perpendicular magnetic recording head, and a magnetic disk drive using these heads.
At present, in a magnetic disk drive used as an external storage for information in information equipment such as a computer or the like, mainly a head which has a read element and a write element is used: a head designed to perform recording by an inductive thin film head, and reproducing by a magnetoresistive effect type head. As a recording system for forming a recording pattern on a medium based on a magnetic flux extending outside a write gap from a recording head, there are two representative types, i.e., an in-plane (longitudinal) recording system and a perpendicular recording system. To achieve a higher recording density, as a future magnetic recording system to replace the conventional in-plane (longitudinal) recording system, a perpendicular magnetic recording system is promising.
In the case of the in-plane (longitudinal) recording system, the magnetic flux extending outside the write gap of the recording head causes a magnetic layer on the medium to be magnetized in a direction equal to/reverse to the advancing direction (trailing direction) of the medium, thus forming a recording pattern on the medium. On the other hand, in the case of the recent perpendicular magnetic recording system devised for the magnetic disk drive or the like, as disclosed in a gazette of Japanese Patent Laid-Open Hei 4 (1992)-57205, a recording head is composed of main and auxiliary poles, a recording medium is mainly a double-layer recording medium, and composed of a recording layer (perpendicular magnetization layer) formed in a side near the recording head, and a soft magnetic underlayer. The main pole, the soft magnetic underlayer and the auxiliary pole of the recording head are magnetically coupled together to form a closed magnetic flux loop. According to this system, if a distance between the main pole of the recording head and the soft magnetic underlayer of the medium is sufficiently smaller than a space between the main and auxiliary poles, a magnetic flux leaked from the main pole magnetizes the recording layer in a film thickness direction, i.e., perpendicularly to a medium surface, passes through the soft magnetic underlayer, and returns to the auxiliary pole. Thus, a recording pattern on the medium is formed in the film thickness direction of the medium, which is the origin of the naming of the perpendicular magnetic recording.
Note that, in the perpendicular magnetic recording system, as in the case of the in-plane (longitudinal) magnetic recording system, as a reproducing head, a magnetoresistive effect element, in particular a GMR head using a huge magnetoresistive effect, a TMR head using a tunnel magnetoresistive effect or the like is used.
FIG. 1 schematically shows a structure of a perpendicular magnetic recording head of the conventional type, which has a read element and a write element. In FIG. 1, the recording head for perpendicular magnetic recording has a structure of being laminated on a reproducing head using a magnetoresistive effect element. The thin film head for perpendicular magnetic recording in FIG. 1 is composed of main and auxiliary poles 1 and 2, a conductor coil 3, and an insulating film 4 for insulating the conductor coil 3, and the main and auxiliary poles 1 and 2. In the head for perpendicular magnetic recording, for the purpose of setting the width of a recording track where signals are recorded by the main pole to be narrow, and a density of a magnetic flux leaked from the main pole to be high, the main pole may be trimmed by FIB or the like after the formation of the main pole by electroplating or the like. Consequently, after the formation of the reproducing head on a substrate, the auxiliary pole, and the main pole are often formed in this order. A big difference between the recording head for perpendicular magnetic recording and the recording head for in-plane magnetic recording is that the head for in-plane recording has a very narrow space (e.g., 0.2 μm) between the main and auxiliary poles when seen from the surface facing to the recording medium, while the head for perpendicular magnetic recording has a larger space (5 to 10 μm).
In FIG. 1, the reproducing head includes a magnetoresistive effect film 5 having electrical resistance changed depending on an applied magnetic field, a magnetoresistive effect element composed of a magnetic domain control film 6 and an electrode 7, an upper shield layer 2 and a lower shield layer 8 for cutting off unnecessary magnetic fields, and a not-shown insulating film for insulating the magnetoresistive effect element and the shields from each other. In the head which has the read element and the write element, shown in FIG. 1, the auxiliary pole 2 of the recording head also serves as an upper shield for the reproducing head. If the auxiliary pole of the recording head and the upper shield of the reproducing head are separately provided, a magnetic separation layer is present between these layers made of magnetic materials.
In the magnetic disk drive, there is a magnetic medium rotating on its axis, and there is a slider includes the foregoing head having the read and write elements mounted. This slider records/reproduces a signal while floating with a constant space kept to the medium surface. In this case, a track for recording/reproducing a signal has a concentric circular structure. Positioning must be controlled to accurately record/reproduce a signal (magnetization pattern) in a track on the medium. Currently, positioning control using a sector servo system is mainly used. In the sector servo system, a circumferential track is divided into a plurality of sectors, a servo area is provided at the head of each sector, after this area, a data area is provided for recording a signal. When recording/reproducing is performed, the magnetic head is positioned on the track by using a servo pattern provided in the sector region. In addition, in the current magnetic disk drive, the root of a suspension having a slider mounted on its tip is fixed, and the suspension has a structure of being moved around its fixed point. Thus, when a signal on a track located near the internal circumference of external circumference of the medium is recorded/reproduced, the slider has a yaw angle with respect to the track.
Compared with the head for in-plane recording, the conventional thin film single pole head for perpendicular magnetic recording has a larger space of 5 to 10 μm between the main and auxiliary poles when seen from a surface facing to the medium, and the reproducing head, the auxiliary pole, and the main pole are formed in this order on the substrate. Thus, a space between the main pole and the reproducing head is 10 μm or more. In the sector servo system, the servo pattern recorded in the servo area is detected by the reproducing head, and positioned on the track. After this operation, a signal is recorded in the data area on the track. When a space between the main pole and the reproducing head becomes wider as described above, it takes time for the recording head to reach the data area after the detection of the servo pattern in the servo area. In other words, a length of an area present between the servo area and the data area, which cannot be used for signal recording, is increased. Consequently, in the perpendicular recording system using the conventional thin film single pole head for perpendicular magnetic recording, compared with the in-plane (longitudinal) recording system, the occupation ratio of the data area per track, i.e., a formatted volume, is reduced.
When a signal is recorded on the track, the slider must be moved in such a way as to move the recording head onto the track after the detection of the servo pattern by the reproducing head located on the track. As a yaw angle is set in a track near the internal circumference or external circumference of the medium, the moving distance of the slider is increased, making it difficult to perform positioning control (servo). When a space is widened between the main pole and the reproducing head, the moving distance of the slider is increased more, making it difficult to design a servo system. Thus, in the perpendicular recording system using the conventional thin film single pole head for perpendicular magnetic recording, servo is more difficult compared with the in-plane (longitudinal) recording system.
In addition, in the perpendicular recording system using the conventional thin film single pole head for perpendicular magnetic recording, the auxiliary pole is formed so as to be on the same recording track of the main pole. Accordingly, as represented by erasure after recording, the recording pattern on the medium is easily affected by a magnetic flux supplied from the main pole, passed through the soft magnetic underlayer of the medium, and returned to the auxiliary pole. Further, since the main pole is laminated after the formation of the auxiliary pole, the number of process steps is increased, extending time for forming the recording head.
Note that, IEEE Trans, Magn., vol. MAG-23, No. 5, pp. 2070-2072 (1987) describes a bulkhead including a plurality of auxiliary poles disposed around a main pole. However, the head described therein is one for both recording and reproducing, and has no elements dedicated for reproducing, such as an MR element. Thus, nothing is suggested regarding a problem caused by the large space between the reproducing element and the main pole, which the invention tries to solve, or a specific method of reducing the space between the reproducing element and the main pole.